The Effect of Alpha Source to Aerosol Distance on the Performance of a Diffusion Charger

This paper discusses the effect of the distance between an a-ray source and a stream of ultrafine aerosol particles on the fraction of charged particles. A simple geometrical model is derived which takes into account the effect of charger walls on (i) the effective extent of the radiation cone, and (ii) the ion losses by Brownian diffusion. The model predicts with reasonable accuracy the relative concentration of ions leaving the charger when no aerosol is present. The experiments demonstrated that the relative concentrations of charged particles at the charger outlet can also be predicted by using the geometrical model developed for ions alone. In spite that the specific ionization of a rays has a maximum at about 3.7 cm from the source, the highest concentrations of charged particles were obtained when the aerosol was made to flow just above the radioactive source (zero separation distance).